The world is on the verge of a revolution that promises to change the way the Internet works and it is guaranteed to change the way the entire world communicates, works and plays. The revolution is the introduction of quality of service (QoS) to the Internet. This QoS revolution is already beginning, because most computer networking products (switches and routers) have already added some type of QoS to their feature sets. Unfortunately, there are many different forms of QoS from which to choose and they are not all compatible with one another. Different standards committees (DiffServ, RSVP, MPLS, etc.) are still deciding which of many different QoS proposals will actually be used in the Internet, and hybrid solutions will likely be developed in the very near future that will enable the QoS revolution.
The change is important, because it will eliminate the current Internet routing model that provides the same “best effort” service to all users, all packets, and all traffic flows. When QoS is enabled in a ubiquitous, end to end fashion across the Internet, differentiated services will be permitted, and all packets will be treated differently. High priority packets will be routed with lower latency and lower jitter, while low priority packets may experience more delay and jitter. The throughput needs of each application will determine the priority associated with its corresponding traffic flows, and it is likely that advanced application programs of the future will dynamically change the priority of traffic flows to match the very needs of the user through the entire duration of the session.
Since all packets will not be passed using the same priority level, it follows that all packets cannot be billed using the same charges in the future either. Future Internet users are likely to pay differently for different classes of service, and they may even be billed on a usage basis, e.g., per-minute, per packet, or per byte, similar to the billing schemes used for long distance telephone service today. The use of high priority traffic flow for an application will undoubtedly result in higher Internet usage costs than the use of low priority traffic flows and service level agreements (SLAs) between the Internet user and their service provider will detail the available priority and throughputs in and their associated costs. These changes in the Internet billing model represent an incredible revenue generating potential for access providers that can provide and bill for these new differentiated services, and multiple system operators (MSOs) are key members of this group.
MSOs are positioned in an ideal location within the Internet to play a major role in the QoS revolution, and they will be able to capitalize on the resulting changes. This is because the MSOs are positioned to act as the QoS gatekeeper into the future Internet. They can perform this function because they have access to each subscriber's service level contract and can appropriately mark the priority of all packets that are injected into the Internet by their subscribers. In fact, the MSOs head end equipment, the cable modem termination system CMTS is actually the first piece of trusted equipment not owned by the subscriber to which subscriber packets must pass on their way to the Internet. The CMTS is positioned at the head end office and it provides basic connectivity between the cable plant and the Internet. FIG. 1 illustrates a simplified cable data system 10 with a CMTS 30. The CMTS 30 is connected through Internet link 40 to the Internet 20. The CMTS 30 is also connected through various cable links 50 to a plurality of subscribers 60.
The MSO also provides customer subscription packages and is able to offer (and bill for) many different subscriber service levels. In addition, if the CMTS equipment permits it, the MSO will also be able to offer dynamic service level upgrades to its subscribers. Features contained within an MSOs CMTS must provide most of these revenue generating QoS capabilities. This will result in even greater increases in revenues if the MSOs can maintain adequate counts on usage of different services levels consumed by its subscribers.
As set forth above, this CMTS provides basic connectivity between the cable plant and the local area network that interfaces to an edge router on the Internet. The CMTS is responsible for appropriately classifying, prioritizing, flow controlling, queuing, scheduling and shaping all the traffic flows between cable data subscribers and the Internet. As a result, this type of service experienced by the cable data subscribers will primarily be determined by the features in the CMTS core.
When selecting a CMTS for cable data deployment or expansion, MSOs have several different options from which to choose. The choice is complicated by a broad spectrum of prices and features such as reliability levels, ease of use, controllability, manageability, observability, support for various interfaces, support for various counts and measurements, support for proprietary features and feature upgrades, vendor service levels, etc. The CMTS selection process is even further complicated by the fact that a particular set of CMTS features that are required in one head end area may actually be undesirable in a different head end area because subscriber usage patterns and traffic profiles within the one region may be entirely different from those in another region.
Nevertheless, there is one CMTS feature that will undoubtedly be desirable and necessary for most of the head end that almost all of the MSOs as cable data service expands into the future. This feature is scalability. When referring to the size of a CMTS, the term scalable can be assigned two different meanings. According to one definition, a scalable CMTS should allow growth along a graduated path from very small sizes to very large sizes without imparting any large costs increments onto the MSO at any step along the graduated growth path. According to a second definition, a scalable CMTS should be capable of reaching the maximum capacity for size permitted by the underlined CMTS technology. For many reasons, MSOs might want to look for both of these scalability features when making their CMTS purchasing decisions.
The first of these features (graduated growth) is desirable in a CMTS because cable data services almost always greeted with incredible popularity when ever it enters a new subscription area. This typically leads to the dramatic increase in subscribers within a very short interval of time. To accommodate the sporadic usage increases, the CMTS must be able to rapidly increase the number of downstream and upstream channels being delivered to the subscribers. Any delay in this channel increase may force an MSO to temporarily over subscribe the existing cable data channels. The densely packed subscribers on the over subscribed channels are likely to complain and/or lose interest in the service giving the competitors with cable data service a chance to steal subscribers.
Even an established cable data service area where the upstream and downstream channel counts have been nicely matched to the current subscriber base, the subscriber demand for bandwidth will continually increase over time as new bandwidth hungry Internet applications are introduced. This increase in bandwidth demand will manifest itself as an increase in the subscription rate for higher service level agreements and that will force the MSOs to pack fewer subscribers on a given channel, and that will again require the CMTS to be able to rapidly increase the number of channels even if it is providing to the same number of customers. This illustrates a second reason why graduated growth is a desirable feature in a MSOs CMTS.
The second definition of scalability (maximum capacity) is also a desirable feature within a CMTS, because the ultimate subscriber rates for cable data service are likely to approach the 20–25% levels within these established service areas. Thus, a typical head end supporting 60,000 cable TV subscribers may need to support up to 15,000 cable data subscribers. If future bandwidth demands limit the MSOs to only 500 cable data subscribers per downstream channel, then the maximum equipped CMTS should be capable of supporting up to 30 downstream channels. In addition, if the typical head end requires 4 upstream channels to be associated with each downstream channel, then the maximally equipped CMTS should be capable of supporting up to 120 upstream channels. Unfortunately, accommodating all of these (30+120)=150 connections out of the CMTS will require a large amount of cabling. Each of the 150 required connections must be transported on a coaxial cable. In a well designed system with high availability, the system repair time should be kept to a minimum, so the bundle of cables emanating from the CMTS will likely be coming from the backside of the system chassis to allow office technicians to rapidly replace faulty circuit cards by pulling them off the front side of the system chassis without having to remove and restore the cabling that emanates from the backside of the chassis.
Another feature that will undoubtedly be required at most feature at CMTS products is flexibility. In particular, CMTS' must be able to accommodate the many different traffic profiles throughout the usage area. This implies that the equipment of the CMTS chassis will be different with each head end office because the equipment must be customized to match the input demands of the customers connected to each head end.
As an example, in some areas, this may require circuit cards that require one upstream channel for each downstream channel also known as 1D:1U circuit cards. In other areas, this may require circuit cards support for upstream channels for each downstream channel which is also known as a 1D:4U circuit card. In still other areas, this may require circuit cards that support each upstream channels with each downstream channel also known as a 1D:8U circuit card. Many other types of useful circuit cards can also be envisioned including, but not limited to, 1D:3U circuit cards, 2D:8U circuit cards, 2D:4U circuit cards, and 2D:2U circuit cards. In general, any type of circuit cards of type nD:nU can be envisioned wherein m and n are non-negative integers.
To make matters even worse, the CMTS chassis within a single head end office is likely to require several different types of front circuit cards to accommodate different traffic profiles on different cables leaving the head end office. Thus, a single CMTS might need to be equipped with b 1D:1U circuit cards, c 1D:4U circuit cards, d 1D:8U circuit cards, e 1D:3U circuit cards, f 2D:8U circuit cards, g 2D:4U circuit cards, h 4D:4U circuit cards and i MD:NU circuit cards where b, c, d, e, f, g, h, i, m and n are non-negative integers.
Given that backside cabling is likely to become more popular over time, as high availability CMTS' become more popular, it is apparent that a fundamental problem will develop. The problem is centered around the difficulties that will be encountered by the cable office technicians that are responsible for correctly installing and maintaining the many cables that must be connected to the backside of the high capacity next generations CMTS chassis. Correct connection for the many cables to the backside of the chassis is itself a difficult task. But this task is exasperated by the inclusion of many different circuit card types that can be equipped in the front side of the chassis. When connecting the cables the office technician will typically not be able to see the type of circuit cards that are equipped in the front side of the chassis. As a result, correct connection of the backside cable will require the technician to remember or record the circuit card equippage (circuit card type and circuit card placement in the front card of the chassis).
Unfortunately, in the hectic environment of a cable head end office, this approach is prone to cabling errors. In its most benign form, a cabling error will merely result in delayed delivery of the service to subscribers while the incorrect system operation that results from the incorrect cabling is diagnosed. In even more catastrophic scenarios, the incorrect cabling can literally damage the equipment on either end of the cable resulting in increased equipment costs and delayed delivery of the service to subscribers. In either case, the result is not desirable, so a technique for reducing the possibility of these cabling errors is likely to be a benefit to the technician and to the head end office.